Calcium-rich Polysaccharide From Lycium Barbarum L.Leaves Affects Water Migration And Gluten Conformation Of Model Gluten Dough

With the improvement of people's living standards,the requirements for bread texture,taste,flavor and appearance are also increasing.Gluten is an important protein in wheat flour that forms a viscoelastic structure in dough and bread.In order to improve the quality of the bread,maintain the good sensory and texture characteristics of the bread,extend the shelf life of the bread and make it completely acceptable to the consumer,many bread improvers are used to improve the structure of the bread and soften the texture of the bread.Therefore,the development and application of natural flour improvers should be paid more attention to.Calcium-rich polysaccharide are properly common in nature,but it is rare to study the effects on gluten.Calcium-rich polysaccharide from Lycium barbarum L.Leaves has many functional properties and can be used as a supplement for trace elements.It may have certain health effects when added to gluten flour,and can be used as a natural and safe flour iinprover.Water is a prerequisite for the formation of good gluten,and gluten conformation also affects the quality of the final product.In this study,the mineral-rich polysaccharide component was extracted from the Lycium barbarum L.Leaves,the polysaccharide component without mineral elements was used as a control,and the two types of polysaccharide components(LP or LP@)were separately added to the gluten flour Mineral-rich polysaccharide from Lycium barbarum L.Leaves affects water migration and gluten conformation of model gluten dough were investigated.The results were as follows:1.The polysaccharide from Lycium barbarum L.Leaves was extracted by hot water extraction method,and the yield was 13.87%.The polysaccharide was further subjected to alcohol precipitation,enzymatic hydrolysis and the like to obtain refined polysaccharide LP,and then the mineral was removed to obtain LP@.The content of uronic acid and calcium in LP was 34.76%and 8.61 mg/g,the content of uronic acid in LP@was 30.40%,and the content of calcium was 0.41 mg/g.2.Effects of two types of polysaccharides from Lycium barbarum L.leaves on gluten water holding capacity.Compared with the blank control group(1.44 g/g),both LP and LP@resulted in a significant decrease in gluten water holding capacity(p<0.05).With the increase of polysaccharide concentration,the water holding capacity of LP@had no significant difference(1.24 g/g-1.20 g/g),and the water holding capacity of LP decreased to 0.88 g/g.This indicates that the presence of minerals will change the water solution near the protein,resulting in the decrease of water holding capacity of gluten protein.3.Effects of two types of polysaccharides form Lycium barbarum L.leaves on the microstructure of gluten protein.According to the results of laser scanning confocal microscopy(CLSM),at low polysaccharide concentrations,both types of polysaccharides from Lycium barbarum L.leaves form a good three-dimensional network.Compared with the blank control group,when the polysaccharide concentration was 8%,the microstructures showed significant differences.LP could not form three-dimensional network structure because of the decrease of water holding capacity of gluten protein.With the increase of polysaccharide concentration in Lycium barbarum L.leaves,at high polysaccharide concentration,both types of polysaccharides make the protein network structure more disordered,more uneven,and become lumpy.This result is due to the dilution of gluten by Lycium barbarum L.polysaccharide and the destruction of disulfide bond.4.Effects of two types of polysaccharides from Lycium barbarum L.leaves on free thiol groups of gluten protein.Compared with the blank control,the content of free sulfhydryl group increased significantly in both types of polysaccharides(p<0.05),LP increased from 0.44 ?mol/g to 1.89?mol/g,and LP@increased from 0.44 ?mol/g to 2.71 ?mol/g.LP is slower than LP@in increasing free sulfhydryl groups in gluten protein.This shows that minerals can cause sulfhydryl oxidation in the process of dough preparation and waking up to a certain extent.5.Effects of two types of polysaccharides from Lycium barbarum L.leaves on the molecular weight of gluten protein.The results of Sodium dodecyl sulphate-polyacrylamide gel electrophoresis(SDS-PAGE)showed that LP and LP@did not affect the molecular weight of glutenin,but mainly caused the instability of gluten structure by affecting the molecular weight of gliadin.LP@can cause the rapid decrease of gliadin bands,indicating that minerals can protect gliadin to a certain extent.6.Effects of two types of polysaccharides from Lycium barbarum L.leaves on water migration of gluten protein.By analyzing the Attenuated total reflection-fourier transform infrared spectroscopy(ATR-FTIR)-OH vibration band(4,000 cm-1-2,700 cm-1),four positive peaks in pure gluten dough were found,which were 3,645 cm-1-3561 cm-1,3,212 cm-1-3,201 cm-1,2,960 cm-1 and 2,890 cm-1,respectively.At low water content(35%),the peak value of LP shifts to the left more than that of LP@,because mineral elements destroy hydrogen bonds,but with the increase of water content,the effect is gradually neutralized.Therefore,the strength of peak value is affected by water content,polysaccharide concentration and minerals.7.The effects of two types of polysaccharides from Lycium barbarum L.leaves on the secondary structure of gluten protein.By analyzing the amide band I(1,700 cm-1-1,600 cm-1)of attenuated total reflection-fourier transform infrared spectroscopy(ATR-FTIR),the secondary structure of gluten protein was obtained.At all water contents,LP at different concentrations resulted in an increase in?-sheet,a decrease in ?-turn and random coil.LP@has the same trend except for random coil.For LP or LP@,with the increase of polysaccharide concentration,the elastic ?-helix structure in gluten structure decreases,and the formation of inelastic ?-sheet reduces the viscoelasticity of dough.Adding LP@can also lead to the transformation of ?-helix structure into ?-sheet and random coil.Random coil,as a disordered secondary structural component,acts together with ?-sheet to destroy the stability of gluten structure.